1. Soluble Salts in Water KI and K 2 CrO 4 : –Potassium iodide and potassium chromate are water-soluble. AgI and PbCrO 4 –Silver iodide and lead chromate and are sparingly soluble: K sp (AgI)=8.5 X 10 -17 K sp (PbCrO 4 )=1.8 X 10 -14

3. Common Ion Effect Silver iodide AgI(s)  Ag + + I - K sp =[Ag + ][I - ] = 8.5 X 10 -17 [Ag + ] = [I - ] = solubility = What if the solution were 0.1M in Ag + ions? What if the solution were 0.1M in I - ions?

4. Common Ion Effect

5. Lead chromate PbCrO 4 (s)  Pb 2+ + CrO 4 2- K sp =[Pb 2+ ][CrO 4 2- ] =1.8 X 10 -14 Let x = solubility of [Pb 2+ ] = [CrO 4 2- ] What if [Pb 2+ ] = 0.1M? What if [CrO 4 2- ] = 0.1M? What if [Pb 2+ ]=[CrO 4 2- ] = 0.1M?

6. Common Ion Effect Calcium fluoride CaF 2 (s)  Ca 2+ (aq) + 2F - (aq) K sp =[Ca 2+ ][2F - ] 2 = 1.7 X 10 -10 Solubility = x = [Ca 2+ ] = 5.6 X 10 -4 K sp =[Ca 2+ ] [2F - ] 2 = (x)(2x) 2 = 4x 3 = 1.7 X 10 -10

7. Selective Precipitation A solution where [Ba 2+ ] = [Ca 2+ ] = 0.1M –Add sulfate ions: K sp (BaSO 4 ) = 10 -10 ; K sp (CaSO 4 ) = 10 -5 Sparingly soluble BaSO 4 and CaSO 4 precipitate. Which salt precipitates first? How much of the first is left in solution when the second begins to precipitate?

8. Electrolytes Conductivity in water is due to hydrated ions moving about. –Water and aqueous sugar solutions –Acetic acid and vinegar –Aqueous salt solutions Experiments –Electrolytes –Nonelectrolytes

9. Autoionization of Water H 2 O(liq) + H 2 O(liq)  H 3 O + + OH -

10. Autoionization of Water H 2 O(liq) + H 2 O(liq)  H 3 O + + OH -

11. Acid-Base Theories Arrhenius HCl  H + + Cl - Could not explain alkalinity of aqueous ammonia Brönsted NH 3 + H 2 O  NH 4 + + OH - HCl + H 2 O  H 3 O + + Cl - Lewis NH 3 + H +  NH 4 +

12. pH Scale Measures acidity of Aqueous Solutions pH = -log[H 3 O + ] by definition pK w = pH + pOH because….K w =[H 3 O + ][OH - ] For neutral solutions… [H 3 O + ] = [OH - ] = 10 -7 M pH = -log[H 3 O + ] pH = 7

14. pH of Aqueous Solutions If [H 3 O + ] = 5.25 x 10 -3 M –Then pH = -log 5.25 x 10 -3 = 2.28 If pH = 5.25 –Then [H 3 O + ] = 10 -5.25 = 5.6 x 10 -6 M And [OH - ] = Kw/[H 3 O + ] = 1.78 x 10 -9 M So pOH = 8.75 And pH = 14 - 8.75 = 5.25

15. pH of Aqueous Solutions When pH is low…… [H 3 O + ] > [OH - ] When pH is neutral….. [H 3 O + ] = [OH - ] When pH is high….. [H 3 O + ] < [OH - ]

16. Dissociation of HA in Water HA + H 2 O  H 3 O + + A - For an acid of the general form HA

20. Indicators HInd + H 2 O  H 3 O + + Ind- Indicator equation

22. Oxides and Hydrides Metallic oxides Na 2 O + H 2 O  2NaOH CaO + H 2 O  Ca(OH) 2 Nonmetallic oxides SO 2 + H 2 O  H 2 SO 3 CO 2 + H 2 O  H 2 CO 3 Metal Hydrides NaH + H 2 O  NaOH + H 2

23. For Strong Acids Aqueous hydrochloric acid solutions HCl + H 2 O  H 3 O + + Cl - 0.1M HCl = 0.1M H 3 O + –Presumption is complete dissociation –pH = 1 Add 10 mL to 990 mL of H 2 O –pH change is… huge!

24. For Weak Acids Aqueous acetic acid solutions HOAc + H 2 O  H 3 O + + OAc - k a =1.75 X 10 -5 0.1M HOAc << 0.1M H 3 O+ Incomplete dissociation: pH = 2.87 Aqueous HF HF + H 2 O  H 3 O + + F - k a =7.2 X 10 -4 and pH = ?

25. For Very Weak Acids Aqueous hydrogen cyanide solutions HCN + H 2 O  H 3 O + + CN - 0.1M HCN <<< 0.1M H 3 O + K a = 4.0 X 10 -10 and pH = 5.2 0.1M NaCNpH = ? 0.1M NaFpH = ? 0.1M NaOAcpH = ?

26. 0.10M Solutions of HA K a pK a pH HCl˜10 7 -7 1 HOAc˜10 -5 5 3 HCN˜10 -11 11 6 H 2 O˜10 -14 14 7 0.10M Solutions of B K b pK b pOH NH 3 ˜10 -5 5 3

27. Solvolysis/Hydrolysis For a weak acid HA….. – the anion is strong and reacts with the solvent in a proton-transfer reaction: A - + H 2 O  HA + OH - For a weak base B….. – the cation ion is strong and reacts with the solvent in a proton-transfer reaction: BH + + H 2 O  B + H 3 O +

28. Hydrolysis Alkaline solutions: NaOAc, NaF, NaCN Acidic solutions: NH 4 Cl Neutral solutions: NH 4 OAc NaCN and Na 2 CO 3 solutions? AlCl 3 and Fe(NO 3 ) 3 solutions? NH 4 CN solutions?

29. pH of 0.10M Aqueous NaOAc NaOAc(s)  Na + (aq) + OAc - (aq) OAc- + H 2 O  HOAc + OH - pOH = 5 and pH =14 - 5 = 9

30. Buffers Solutions of a weak acid and its conjugate base: HA + H 2 O  H 3 O + + A - Solutions of a weak base and its conjugate acid: B + H 2 O  BH + + OH -

31. Buffers Buffers act across an [A-]/[HA] range of 10/1 to 1/10 … or 2 pH units:

32. Buffers Aqueous acetic acid solutions HOAc + H 2 O  H 3 O + + OAc - For 0.1M HOAc: pH = 2.87 For HOAc/NaOAc buffer: pH = pKa = 4.76 PROBLEM: Add 50mL 0.10M HCl to 950 mL H 2 O containing 0.050 mole HOAc and 0.050 mole NaOAc. –Buffer soaks up the acid –pH change is relatively small.

33. Polyprotic Acids Carbonic acid (H 2 CO 3 ) K a H 2 CO 3 + H 2 O  H 3 O + + HCO 3 - 10 -7 HCO 3 - + H 2 O  H 3 O + + CO 3 2- 10 -11 –Acidity is essentially supplied by K a (1) –Blood is buffered by [CO 2 ]/[HCO 3 - ]

35. Polyprotic Acids –Sulfuric acid (H 2 SO 4 )pK a H 2 SO 4 + H 2 O  H 3 O + + HSO 4 - -5HSO 4 - + H 2 O  H 3 O + + SO 4 2- 2 –Phosphoric acid (H 3 PO 4 ) pK a H 3 PO 4 + H 2 O  H 3 O + + H 2 PO 4 - 2.1 H 2 PO 4 - + H 2 O  H 3 O + + HPO 4 2- 7.2 HPO 4 - + H 2 O  H 3 O + + PO 4 3- 12.3 Note:K values are lower by several orders of magnitude due to increasing negative charge.

36. Titration curves

39. Finding K a for Weak Acids –For a monoprotic acid, at the mid-point, [HA] = [A-] pH = pKa

40. ACID/BASE ISSUES Acid rain and coal mine run-off: –Kentucky, West Virginia, Indiana, Illinois, Minnesota… many places. Industrial acid/base run-off in rivers: –Raritan River is one of many. Acid rain and steel manufacture Acid: –Adirondks and Great Smokys –Illinois and Indiana mills

41. ACID/BASE ISSUES Corrosion –N and S oxides –Acidic oxides Particulates in the air: –Donora, Pennsylvania –Dupont “nylon” in downtown Chicago

42. Lessons from History The disadvantage of men not knowing the past is that they do not know the present. - G. K. Chesterton

44. Complex Ion Formation 1)AgI(s)  Ag + (aq) + I - (aq) K sp = [Ag + ][I - ] = 10 -16 2)Ag + (aq) + 2NH 3 (aq)  Ag(NH 3 ) 2 + (aq) 3) AgI(s) + 2NH 3 (aq)  Ag(NH 3 ) 2 + (aq) + I - (aq)

45. Complex ion formation AgCl ppt dissolves in aq. NH 3 AgBr ppt dissolves in aq. NH 3 but with difficulty AgI ppt does not dissolve in aq. NH 3 but does dissolve in aq. CN -

46. Dissolving Precipitates AgCl –Add ammonia Forms soluble Ag(NH 3 ) + complex AgBr –Add lots of ammonia Forms soluble Ag(NH 3 ) + complex AgI –Add cyanide ion Forms soluble Ag(CN) 2 - complex